1. Field of the Invention
This invention is directed toward improved synthetic grass surfaces. The invention is more particularly directed toward improved, synthetic grass sports surfaces. The invention is also directed toward a method of making an improved synthetic grass sports surface, and an apparatus for carrying out the method. The invention is further directed toward an improved synthetic grass sports surface having playing lines formed in its top surface and to a method of making the lined surface.
2. Description of the Prior Art
Synthetic grass sports surfaces are well known. They are used to replace natural grass surfaces which do not stand up well to wear and which require a great deal of maintenance. Also, natural grass surfaces do not grow well in partly or fully enclosed sports stadiums. The synthetic grass surfaces stand up to wear much better than the natural grass surfaces, do not require as much maintenance, and can be used in closed stadiums. Some synthetic grass surfaces comprise rows of strips or ribbons of synthetic material, extending vertically from a backing mat with particulate material infilled in between the ribbons on the mat. The ribbons of synthetic material usually extend a short distance above the layer of particulate material and represent blades of grass. The particulate material usually comprises sand, as shown by way of example in U.S. Pat. Nos. 3,995,079, 1976, Haas, Jr. and 4,389,435, 1983, Haas, Jr., but can comprise other materials or a mixture of sand and other materials, as shown in U.S. Pat. No. 4,337,283, 1982, Haas, Jr., by way of example. The particulate material provides resiliency to the synthetic grass surfaces, and the surfaces are often laid on a resilient pad to provide further resiliency to the surfaces.
The known sand-filled synthetic grass sports surfaces have some disadvantages. The surfaces usually become hard after extended use because the sand, between the rows of ribbons, becomes compacted. Compacting occurs, in part, because the rows of ribbons are quite close together, and the sand cannot spread a great deal laterally during use. Compacting also occurs, in part, because the close spacing of the ribbon rows traps debris, worn and torn off the ribbons, in the sand, even when the particulate material comprises rounded sand particles. With an increase in compaction, the surface becomes progressively harder and less resilient. The performance of the surface is shortened, and it has lessened playing qualities. The surfaces also become harder after use because the resilient pads, if used, slowly collapse under use, becoming denser. Removal and replacement of the compacted particulate material, or even loosening of it, is difficult because of the close spacing of the rows of ribbons. It can require expensive equipment to remove and replace the compacted particulate material, or even loosen it, and this adds to the cost of maintaining the surface.
Another problem with the known synthetic grass sport surfaces is the problem of drainage. Water flow through the surfaces has generally been slow. The ribbons are usually attached to the mat by tufting them through the mat, and then the bottom of the mat is coated with a bonding layer to bond the ends of the ribbons to the mat. The bonding layer is non-porous. To provide adequate porosity, the coated mat is punctured to provide holes. However, the particulate material often flows into these holes, plugging them up and thus reducing the drainage qualities of the surface. The loss of the particulate material into and through the holes also requires that it be replaced on top of the mat, adding to the cost of maintaining these surfaces. Compaction of the surface also inhibits drainage.
The known synthetic surfaces also have relatively poor playing qualities. When infilled with rounded sand particles more rounded than angular, because the rounded particles are thought to compact less and cause less abrasion, the surface can become too slippery, particularly when the ribbons are only slightly longer than the thickness of the layer of particulate material. Also, the closely spaced fine ribbons, if penetrated, can tightly grip the cleats and do not tear as easily as grass, thus making release of the cleats more difficult and making playing on the surface more difficult and dangerous than when playing on grass. If a player""s cleats do not release easily, he could injure his leg, ankle, or knee. It has also been found that if the athlete""s cleat penetrates a seam area, the chances of the shoe not being released or allowed to pivot is much greater.
The known synthetic surfaces, with closely spaced rows of ribbons, also increase the speed of a rolling ball from the speed with which it rolls on natural grass. The closely spaced ribbons create an almost solid, low resistance surface for a rolling ball, thus adversely affecting the playing qualities of the surface. If the surfaces are employed with a resilient base pad, balls bounce more on the surfaces than on grass, subtly changing the nature of the game. The low resistance surface also makes it more slippery for tennis players.
The known surfaces have other disadvantages. Usually the ribbons employed are quite narrow, and they can curl creating an appearance unlike grass. The narrow ribbons also abrade easier, creating debris that can increase compaction of the surface. The close spacing of the ribbon rows also causes skin abrasion on players falling or sliding on the surfaces.
It is the purpose of the present invention to provide an improved synthetic grass sports surface that is more resilient, and remains more resilient for a longer period of time, than known synthetic grass surfaces.
It is another purpose of the present invention to provide improved synthetic grass sports surfaces that have improved drainage properties and improved playing properties.
It is yet another purpose of the present invention to provide improved synthetic playing surfaces that are relatively less expensive to manufacture, to install, and particularly to maintain.
It is still another purpose of the present invention to provide synthetic playing surfaces that are less abrasive, easier to mark with lines, and easier to seam.
It is another purpose of the present invention to provide a method for making one embodiment of the present invention having improved drainage properties and a machine for carrying out the method.
In accordance with the present invention, it has been found that an improved synthetic grass surface can be provided by employing relatively widely spaced rows of ribbons. The wider spacing of the ribbon rows reduces the compaction of the infill that normally occurs with more closely spaced rows, thus extending the life of the surface with respect to resiliency. Reduced compaction also ensures better drainage. Wider row spacing should also ensure less wear and abrasion of the ribbons, extending the life of the surface and minimizing the formation of ribbon debris which affects compaction and drainage. Wider row spacing also allows better cleat penetration and allows the cleats to release easier, thus improving the playing qualities and reducing the risk of injury. Wider ribbon row spacing can also cause balls on the surface to roll more like they roll on grass, thus improving playing qualities. Wider ribbon row spacing also makes it easier to loosen the particulate material if it does start to compact, and to clean or replace it. Wider ribbon row spacing also reduces abrasion to the players when contacting the surface. Wider ribbon row spacing can make it easier to seam the surface.
In accordance with the present invention, it has also been found that an improved synthetic grass surface can be provided by providing ribbons having a length about twice as long as the spacing between the rows of ribbons. The present invention employs ribbons that are quite long compared to the ribbons now employed. The longer ribbons allow a thicker layer of particulate material to be used which can eliminate the need for a resilient pad and make installation of the surface simpler and cheaper. A thicker layer of particulate material or infill promotes better drainage because of the higher water head created by water on the synthetic grass. Preferably, the layer of particulate material has a thickness at least two-thirds the length of the ribbons. The longer ribbons can also provide more ribbon material above the infill for certain sport surfaces, creating a more realistic grass-like surface that, in combination with the wider spacing of the ribbon rows, allows a player""s cleats to both penetrate the surface for traction but also easily release. The player""s cleats can move the ribbons and infill material sideways to allow easier release.
In accordance with another embodiment of the present invention, the improved synthetic grass surface is constructed to have improved drainage qualities provided by the manner and pattern in which the ribbons are attached. In accordance with the present invention, the rows of ribbons are attached by strips of bonding material applied to the back of the mat. The strips of bonding material are spaced apart and leave areas of the mat uncoated. Since the mat in this embodiment is porous, the uncoated areas provide for excellent drainage. Providing a surface with a relatively large spacing between the rows of ribbons allows strips of bonding material to be provided with relatively wide porous areas of mat between them. The invention is also directed to an apparatus to simply and easily apply the bonding strips to the backing.
Improved drainage properties are also obtained by having at least one of the backing layers, a needle punched fabric, provided with fuzzy fibers on one or both surfaces. The fuzzy fibers improve the drainage qualities of the backing layer, and thus of the surface, since the fuzzy fiber ends wick away the moisture.
Also in accordance with the present invention, the surface is provided with an improved infill layer of particulate material. The infill preferably comprises a mixture of silica sand and cryogenically ground rubber particles. The cryogenically ground rubber particles wet more easily than non-cryogenically ground rubber particles and thus allow faster drainage. The ratio of sand to rubber can be varied depending on the end use of the surface; the more resilient surface required, the more rubber employed. The cryogenically ground rubber is less angular than non-cryogenically ground rubber and has less tendency to allow water, and microscopic air bubbles carried by the water, to attach to it. Thus, there is less tendency for the rubber particles to float upwardly when the surface is flooded which could result in the loss of material and a change in the playing qualities of the surface.
The surface, in accordance with the present invention, is also provided with line forming means, the lines being used to mark the playing surface for the sport being played. Examples of such lines are the yardage lines used in the game of football which traverse the field at regular intervals. These lines are usually laid down on top of the field with chalk or other similar marking material. In accordance with the present invention, the surface can be provided with permanent lines seamed in the surface. The lines are seamed by the manner in which the backing layers are joined together.
The invention is particularly directed toward a synthetic grass surface having a flexible, backing layer and parallel rows of synthetic ribbons representing blades of grass projecting vertically from the backing layer, the rows of ribbons spaced from each other from between five-eighths and two and one-quarter inches apart. The surface includes a relatively thick layer of particulate material on the backing layer between the ribbons and supporting them in a relatively upright position relative to the backing layer.
The invention is further particularly directed toward a synthetic grass surface having a flexible, backing layer and parallel rows of synthetic ribbons representing blades of grass projecting upwardly from the backing layer. The surface includes a relatively thick layer of particulate material on the backing layer supporting the ribbons in a relatively upright position relative to the backing layer, the particulate material comprising a mixture of cryogenically ground rubber and silica sand.
Cryogenically ground rubber means rubber particles which have been made from the process of reducing rubber from used tires by a cryogenically ground rubber method. The fragmenting of the rubber when it is frozen results in rubber particles with smoother surfaces less jagged as would occur with non-cryogenically ground rubber.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.